A gravity gradiometer is disclosed in our International Patent Application No. PCT/AU2006/001269 and several concurrently filed applications. The content of International Patent Application No. PCT/AU2006/001269 is incorporated into this specification by this reference.
Gravimeters are widely used in geological exploration to measure the first derivatives of the earth's gravitational field. Whilst some advances have been made in developing gravimeters which can measure the first derivatives of the earth's gravitational field because of the difficulty in distinguishing spatial variations of the field from temporal fluctuations of accelerations of a moving vehicle, these measurements can usually be made to sufficient precision for useful exploration only with land-based stationary instruments.
Gravity gradiometers (as distinct from gravimeters) are used to measure the second derivative of the gravitational field and use a sensor which is required to measure the differences between gravitational forces down to one part in 1012 of normal gravity.
Typically such devices have been used to attempt to locate deposits such as ore deposits including iron ore and geological structures bearing hydrocarbons.
The above-mentioned gradiometer has a sensor in the form of a sensor mass which is pivotally mounted for movement in response to the gravity gradient.
Gravity gradiometers of the type described in the above International applications have super-conducting components which are housed in a vacuum canister which in turn is located in a Dewar. The componentry includes SQUID devices and other circuitry and in order to provide signals to external measuring equipment outside the Dewar, and connectors are provided to connect internal wiring within the Dewar to that equipment. Because of the super-conducting nature of the circuitry, the internal circuitry must be protected from RF interference from outside sources, such as telephone and television signals, etc. which result in currents passing from the external circuitry into the internal super-conducting circuitry which can result in incorrect measurements being made or significant noise in the measurement signals.